1. Field of the Invention
The present invention relates to a switchgear control apparatus for controlling opening/closing operation of each circuit breaker of a switchgear which disconnects and reconnects a power transmission line and, more particularly, the invention is concerned with a technique for suppressing a surge voltage which occurs when a power line is reconnected under no-load conditions.
2. Description of the Background Art
Conventionally, a controlled switching technique is used for suppressing a surge voltage which occurs when a power transmission line once disconnected is reconnected under no-load conditions. This control technique involves detecting a voltage across opposite terminals of a switchgear and closing the switchgear at a point in time when the opposite switchgear terminals have a common polarity as described in Japanese Unexamined Patent Publication Nos. 1980-151724 and 1980-151725, for instance.
In the event of so-called high-speed reclosing of a power transmission line at zero load, an electric charge which has been accumulated therein before circuit interruption is scarcely discharged and remains almost entirely in the transmission line, thus producing a residual DC voltage. A special type of voltage sensor system made up of a capacitive voltage divider, for example, is required for exactly measuring this residual voltage as mentioned in the above-cited Publications. However, such a special type of voltage sensor system is not provided in a generally used power system so that the conventional control technique is not useful enough from a practical point of view.